The present invention relates to a pressure regulating valve for hydraulic brake systems for vehicles comprising a housing with a pressure chamber communicating with a master brake cylinder through an inlet and with at least one brake-actuating cylinder through an outlet, a differential piston arranged in the pressure chamber and acted upon towards the outlet by a spring, the piston's larger surface being exposed to the outlet pressure while its smaller surface is exposed to the inlet pressure, an elastomeric sealing ring arranged in the pressure chamber between inlet and outlet and bounding a first passageway which extends from the inlet to the outlet and is adapted to be closed by axial displacement of the differential piston on attainment of a pressure in the inlet and the outlet which is predetermined by the differential piston surfaces and the spring, the sealing ring including on its side close to the inlet a sealing lip cooperating with the wall of the pressure chamber and closing a second passageway in the event of a pressure gradient from the inlet to the outlet and opening it in the event of a pressure gradient in the opposite direction, the sealing ring being held in pressure-sealed engagement with the differential piston, is supported on a shoulder of the differential piston adjacent the outlet chamber, forming the first passageway with its end surface adjacent the inlet chamber and with an opposite sealing surface, and in that a connecting channel in the differential piston connects the first passageway to the outlet chamber.
Pressure regulating valves of this type are preferably inserted in the brake line between the master brake cylinder and the brake-actuating cylinder of the rear wheels in order to reduce in higher brake pressure ranges the brake pressure of the rear wheel brakes relative to that of the front wheel brakes to take into account the dynamic axle load transfer while braking. These pressure regulating valves are usually installed in an appropriate position in the vehicle and connected by brake lines with the master and the wheel brake cylinders.
The conventional brake unit having functional elements of simple construction but separately arranged is in many respects not satisfactory, since each functional element requires a separate housing and corresponding connecting lines. High costs for material, machining and assembly will be incurred thereby.
German Patent DE-AS No. 1,430,226 discloses a pressure regulating valve which is integrated in a wheel brake cylinder. However, the construction of this device is so complicated that it was not successful in practice.